Display device

ABSTRACT

According to one embodiment, a display device includes a first substrate including a first pixel electrode disposed on a first color pixel of red, a second pixel electrode disposed on a second color pixel of green, a third pixel electrode disposed on a third color pixel of blue, and a fourth pixel electrode disposed on a fourth color pixel of white, a second substrate including a common electrode, and a liquid crystal layer held between the first substrate and the second substrate, wherein a top voltage applied to the fourth color pixel to correspond to a maximum gradation value is set to be less than a top voltage applied to each of the first color pixel and the second color pixel to correspond to respective maximum gradation values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2013-217439, filed Oct. 18, 2013, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

Methods for improving display luminance in color display devices havebeen proposed. As an example, there is a liquid crystal display devicein which one unit pixel is constituted by arranging a red (R) colorpixel, a green color (G) pixel, a blue color (B) pixel and a white color(W) pixel in a row direction in a predetermined order.

In recent years, liquid crystal display devices with a verticalalignment (VA) mode and an in-plane switching (IPS) mode are developed.In the VA mode, liquid crystal molecules are aligned vertically in theinitial state and then inclined while a voltage is being applied theretoin order to vary birefringence. The VA mode realizes transmittance(white) and non-transmittance (black) using this birefringence varied bythe inclination. In the IPS mode, liquid crystal molecules are alignedin-plane to be parallel with a substrate major surface in the initialstate and then rotated in-plane while a voltage is being applied theretoin order to vary birefringence. The IPS mode realizes transmittance(white) and non-transmittance (black) using this birefringence varied bythe rotation.

In the VA mode, the liquid crystal molecules between pixels of differentcolors do not change their original inclination significantly ascompared to the IPS mode. Thus, the VA mode can narrow down the lightshielding widths between the color pixels for higher aperture ratio andluminescence. On the other hand, optical rotatory dispersion orwavelength dispersion in the liquid crystal layer affects pixel hues inaccordance with the inclination of the liquid crystal molecules. When aunit pixel is composed of general three color pixels of red, green andblue, a voltage value of each of red color pixel, green color pixel, andblue color pixel is adjusted to correspond to gradation values forachieving a chromaticity maintaining a white balance. However, when aunit pixel is composed of four color pixels of red, green, blue andwhite, a blue shift phenomenon in which the hue of the white color pixelchanges bluish appears conspicuously, and a sufficient chromaticityadjustment in three color pixels of red, green and blue becomesdifficult.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view which schematically illustrates a structure and anequivalent circuit of a liquid crystal display panel LPN whichconstitutes a display device according to an embodiment.

FIG. 2 is a plan view which schematically illustrates a structureexample of one pixel PX of an array substrate AR which is applicable tothe display device of the embodiment.

FIG. 3 is a plan view which schematically illustrates a structureexample of one pixel PX of a counter-substrate CT which is applicable tothe display device of the embodiment.

FIG. 4 is a view which schematically illustrates a cross-sectionalstructure of the liquid crystal display panel LPN in an active areaincluding a switching element SW shown in FIG. 2.

FIG. 5 is a plan view which schematically illustrates an example of alayout of pixels and color filters in the embodiment.

FIG. 6 is a plan view which schematically illustrates a structureexample of an array substrate AR to which the color filters shown inFIG. 5 are applied.

FIG. 7 is a plan view which schematically illustrates a structureexample of a second common electrode CE2 disposed in a counter substrateCT opposed to the array substrate AR shown in FIG. 6.

FIG. 8 is a view which conceptually illustrates a chromaticity shiftrelative to applied voltages in white color pixels.

FIG. 9 is a plan view which schematically illustrates another structureexample of a layout of pixels and color filters in the embodiment.

FIG. 10 is a plan view which schematically illustrates another structureexample of a layout of pixels and color filters in the embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device includes: afirst substrate including a first pixel electrode disposed on a firstcolor pixel of red, a second pixel electrode disposed on a second colorpixel of green, a third pixel electrode disposed on a third color pixelof blue, and a fourth pixel electrode disposed on a fourth color pixelof white; a second substrate including a common electrode which isopposed to the first, second, third, and fourth pixel electrodes; and aliquid crystal layer held between the first substrate and the secondsubstrate, wherein a top voltage applied to the fourth color pixel tocorrespond to a maximum gradation value is set to be less than a topvoltage applied to each of the first color pixel and the second colorpixel to correspond to respective maximum gradation values.

According to another embodiment, display device includes: a firstsubstrate including a first common electrode, an interlayer insulatingfilm covering the first common electrode, a first pixel electrodedisposed on a first color pixel of red on the interlayer insulatingfilm, a second pixel electrode disposed on a second color pixel of greenin the interlayer insulating film, a third pixel electrode disposed on athird color pixel of blue on the interlayer insulating film, and afourth pixel electrode disposed on a fourth color pixel of white on theinterlayer insulating film; a second substrate including a second commonelectrode which is opposed to the first pixel electrode, the secondpixel electrode, the third pixel electrode, and the fourth pixelelectrode; and a liquid crystal layer held between the first substrateand the second substrate, wherein a top voltage applied to the fourthcolor pixel to correspond to a maximum gradation value is set to be lessthan a top voltage applied to each of the first color pixel and thesecond color pixel to correspond to respective maximum gradation values.

Embodiments will now be described in detail with reference to theaccompanying drawings. In the drawings, structural elements having thesame or similar functions are denoted by like reference numbers, and anoverlapping description is omitted.

FIG. 1 is a view which schematically illustrates a structure and anequivalent circuit of a liquid crystal display panel LPN whichconstitutes a display device according to an embodiment.

Specifically, the display device includes an active-matrix-type liquidcrystal display panel LPN. The liquid crystal display panel LPN includesan array substrate AR which is a first substrate, a counter-substrate CTwhich is a second substrate that is disposed to be opposed to the arraysubstrate AR, and a liquid crystal layer LQ which is held between thearray substrate AR and the counter-substrate CT. The liquid crystaldisplay panel LPN includes an active area ACT which displays an image.The active area ACT corresponds to a region where the liquid crystallayer LQ is held between the array substrate AR and thecounter-substrate CT, has a rectangular shape, for instance, and iscomposed of a plurality of pixels PX which are arrayed in a matrix.

The array substrate AR includes, in the active area ACT, a plurality ofgate lines G (G1 to Gn) extending in a first direction X, a plurality ofsource lines S (S1 to Sm) extending in a second direction Y crossing thefirst direction X, a switching element SW which is electricallyconnected to the gate line G and source line S in each pixel PX, a pixelelectrode PE which is electrically connected to the switching element SWin each pixel PX, and a first common electrode CE1 which is opposed tothe pixel electrode PE. A storage capacitor CS is formed, for example,between the first common electrode CE1 and the pixel electrode PE.

On the other hand, the counter-substrate CT includes, for example, asecond common electrode CE2 which is opposed to the pixel electrode PEvia the liquid crystal layer LQ.

Each of the gate lines G is led out to the outside of the active areaACT and is connected to a first driving circuit GD. Each of the sourcelines S is led out to the outside of the active area ACT and isconnected to a second driving circuit SD. At least parts of the firstdriving circuit GD and second driving circuit SD are formed on, forexample, the array substrate AR, and are connected to a driving IC chip2. The driving IC chip 2 incorporates a controller which controls thefirst driving circuit GD and second driving circuit SD, and functions asa signal supply source for supplying necessary signals for driving theliquid crystal display panel LPN. In the example illustrated, thedriving IC chip 2 is mounted on the array substrate AR, on the outsideof the active area ACT of the liquid crystal display panel LPN.

The driving IC chip 2 stores a controller for the first driving circuitGD and the second driving circuit SD and functions as a signal supplysource which supplies necessary signals for driving the liquid crystaldisplay panel LPN. The driving IC chip 2 further functions as a voltageapplier which applies a voltage to each pixel PX, specifically, eachpixel PX color by color to correspond to gradation values. The drivingIC chip 2 stores, for example, a memory which memorizes a voltage rangeset for each color pixel and a voltage value allocated to each gradationvalue within the voltage range. Both the bottom voltage and the topvoltage of the utilizable voltage range are set based on a V-Tcharacteristic which is an applied voltage relative to a transmittanceof each color pixel. The voltage value of each gradation value isallocated within the set voltage range. Note that the voltage range andthe voltage value of each gradation value may be stored in a differentmemory instead of such a driving IC chip.

The first common electrode CE1 and second common electrode CE2 have thesame potential, and each of them extends over substantially the entiretyof the active area ACT and is formed commonly over a plurality of pixelsPX. The first common electrode CE1 and second common electrode CE2 areled out to the outside of the active area ACT and are connected to apower supply module Vcom. The power supply module Vcom is formed, forexample, on the array substrate AR on the outside of the active areaACT, and is electrically connected to the first common electrode CE1 andalso electrically connected to the second common electrode CE2 via anelectrically conductive member (not shown). At the power supply moduleVcom, for example, a common potential is supplied to the first commonelectrode CE1 and second common electrode CE2.

FIG. 2 is a plan view which schematically shows a structure example ofone pixel PX of the array substrate AR which is applicable to thedisplay device of the embodiment.

The array substrate AR includes a gate line G1, a source line S1, asource line S2, a switching element SW, a first common electrode CE1,and a pixel electrode PE, etc. In the example illustrated, as indicatedby a broken line in FIG. 2, the pixel PX has a rectangular shape with apair of short sides parallel to the first direction X, and a pair oflong sides parallel to the second direction Y.

The gate line G1 extends linearly in the first direction X. The sourceline S1 and source line S2 are disposed with a distance in the firstdirection X, and extend linearly in the second direction Y,respectively. The length of the pixel PX in the first direction X issubstantially equal to the pitch of neighboring source lines in thefirst direction X. The length of the pixel PX in the second direction Yis substantially equal to the pitch of neighboring gate lines in thesecond direction Y.

In the pixel PX illustrated, the source line S1 is located at a leftside end portion, and is disposed to extend over a boundary between thepixel PX and a pixel neighboring on the left side. The source line S2 islocated at a right side end portion, and is disposed to extend over aboundary between the pixel PX and a pixel neighboring on the right side.The gate line G1 is disposed in a manner to cross a central portion ofthe pixel PX. In the present embodiment, as illustrated, there is nostorage capacitance line which crosses the pixel PX for forming astorage capacitance CS.

The switching element SW is composed of, for example, an n-channelthin-film transistor (TFT). Although a detailed illustration is omitted,the switching element SW includes a semiconductor layer of, e.g.polysilicon, a gate electrode electrically connected to the gate lineG1, a source electrode which is connected to the source line S1 and isput in contact with the semiconductor layer, and a drain electrode WDwhich is in contact with the semiconductor layer.

For example, as indicated by lower-right hatching lines in the Figure,the first common electrode CE1 is disposed over substantially theentirety of the pixel PX, and further extends from the pixel PX beyondthe source line S1 and source line S2 in the first direction X andextends in the second direction Y. Specifically, the first commonelectrode CE1 is opposed to the source line S1 and source line S2 and isformed continuously over pixels neighboring the pixel PX in the firstdirection X. In addition, the first common electrode CE1 is formedcontinuously over pixels neighboring the pixel PX in the seconddirection Y. Furthermore, although not described in detail, the firstcommon electrode CE1 is disposed over substantially the entirety of theactive area which displays an image, and a part thereof is led out tothe outside of the active area and electrically connected to the powersupply module, as described above. It should be noted, however, that anopening OP for exposing the drain electrode WD is formed in the firstcommon electrode CE1.

In the meantime, the first common electrode CE1 may be formed such that,while the first common electrode CE1 is disposed over substantially theentirety of the pixel PX, the first common electrode CE1 is madediscontinuous at an area overlapping the gate line G1, the first commonelectrode CE1 extends from the pixel PX over the source line S1 andsource line S2 in the first direction X, the first common electrode CE1is opposed to the source line S1 and source line S2, and the firstcommon electrode CE1 is continuously formed in a strip shape over pixelsneighboring the pixel PX in the first direction X. In this case, too,the first common electrode CE1 is led out to the outside of the activearea which displays an image, and is electrically connected to the powersupply module, as described above.

As indicated by upper-right hatching lines in the Figure, the pixelelectrode PE is formed in an island shape in the pixel PX, and isopposed to the first common electrode CE1. Incidentally, in the exampleillustrated, although only the pixel electrode PE disposed in the pixelPX is depicted, pixel electrodes are also disposed in other pixelsneighboring the pixel PX in the first direction X and second directionY. The pixel electrode PE is electrically connected to the drainelectrode WD of the switching element SW via a contact hole CH. Theshape of the pixel electrode PE illustrated corresponds to, for example,the shape of the pixel PX, and is a rectangular shape having a lesslength in the first direction X than in the second direction Y. Thecontact hole CH is located at a substantially central part of the pixelelectrode PE. Incidentally, a part of the pixel electrode PE may extendto positions overlapping the source line S1 and source line S2.

In the present embodiment, the structure of each pixel of the activearea is identical to the above-described structure example. However, theactive area may include pixels of different pixel sizes, i.e. differentlengths in the first direction X and second direction Y.

FIG. 3 is a plan view which schematically shows a structure example ofone pixel PX of the counter-substrate CT which is applicable to thedisplay device of the embodiment. FIG. 3 shows only structural partsthat are necessary for the description, and the source line S1, sourceline S2, gate line G1, and pixel electrode PE, which are main parts ofthe array substrate, are indicated by broken lines, and the depiction ofthe first common electrode is omitted.

The counter-substrate CT includes a second common electrode CE2. Thesecond common electrode CE2 is disposed in the pixel PX, and is opposedto the pixel electrode PE. In addition, the second common electrode CE2extends from the pixel PX in the first direction X and the seconddirection Y, and is located also above the source line S1 and sourceline S2. Specifically, although not described in detail, the secondcommon electrode CE2 is disposed continuously over pixels neighboring onthe right side and left side along the first direction X of the pixelPX, and pixels neighboring on the upper side and lower side along thesecond direction Y of the pixel PX. Furthermore, although not describedin detail, the second common electrode CE2 is disposed over almost theentirety of the active area.

A slit SL is formed in the second common electrode CE2 at a positionopposed to the pixel electrode PE. In the example illustrated, the slitSL is formed in a strip shape extending in the second direction Y, andis located at a substantially central part of the pixel PX. Such a slitSL functions mainly as an alignment controller which controls thealignment of the liquid crystal molecules. The alignment controller isnot limited to such a slit and, as long as it controls the alignment ofliquid crystal molecules, the alignment controller can be formedarbitrarily, namely a projection on the second common electrode CE2 andthe like. Furthermore, the shape of the slit SL is not limited to theexample illustrated and may be formed in a cross shape.

FIG. 4 is a view which schematically illustrates a cross-sectionalstructure of the liquid crystal display panel LPN in the active areaincluding the switching element SW shown in FIG. 2.

The array substrate AR is formed by using a first insulative substrate10 having light transmissivity, such as a glass substrate or a resinsubstrate. The array substrate AR includes, on that side of the firstinsulative substrate 10, which is opposed to the counter-substrate CT, aswitching element SW, a first common electrode CE1, a pixel electrodePE, a first insulating film 11, a second insulating film 12, a thirdinsulating film 13, a fourth insulating film 14, and a first verticalalignment film AL1, etc.

In the example illustrated, the switching element SW is a thin-filmtransistor of a top gate type. The switching element SW includes asemiconductor layer SC which is disposed on the first insulativesubstrate 10. In the meantime, an undercoat layer, which is aninsulating film, may be interposed between the first insulativesubstrate 10 and the semiconductor layer SC. The semiconductor layer SCis covered with the first insulating film 11. The first insulating film11 is also disposed on the first insulative substrate 10. This firstinsulating film 11 is formed of, for example, an inorganic material suchas silicon nitride.

A gate electrode WG of the switching element SW is formed on the firstinsulating film 11, and is located immediately above the semiconductorlayer SC. The gate electrode WG is electrically connected to the gateline G1 (or formed integral with the gate line G1) and is covered withthe second insulating film 12. The second insulating film 12 is alsodisposed on the first insulating film 11. This second insulating film 12is formed of, for example, an inorganic material such astetraethoxysilane (TEOS).

A source electrode WS and a drain electrode WD of the switching elementSW are formed on the second insulating film 12. The source line S1 andsource line S2 are similarly formed on the second insulating film 12.The source electrode WS illustrated is electrically connected to thesource line S1 (or formed integral with the source line S1). The sourceelectrode WS and drain electrode WD are put in contact with thesemiconductor layer SC via contact holes penetrating the firstinsulating film 11 and second insulating film 12. The switching elementSW with this structure, as well as the source line S1 and source lineS2, is covered with the third insulating film 13. The third insulatingfilm 13 is also disposed on the second insulating film 12. This thirdinsulating film 13 is formed of, for example, a transparent resinmaterial.

The first common electrode CE1 extends over the third insulating film13. As illustrated in the Figure, the first common electrode CE1 coversthe upper side of the source line S1 and source line S2, and extendstoward neighboring pixels. The first common electrode CE1 is formed of atransparent, electrically conductive material such as indium tin oxide(ITO) or indium zinc oxide (IZO). The fourth insulating film 14 isdisposed on the first common electrode CE1. A contact hole CH, whichpenetrates to the drain electrode WD, is formed in the third insulatingfilm 13 and fourth insulating film 14. The fourth insulating film 14 hasa less thickness than the third insulating film 13, and is formed of,for example, an inorganic material such as silicon nitride. The fourthinsulating film 14 corresponds to an interlayer insulating film whichcovers the first common electrode CE1.

The pixel electrode PE is formed in an island shape on the fourthinsulating film 14 and is opposed to the first common electrode CE1. Thepixel electrode PE is electrically connected to the drain electrode WDof the switching element SW via the contact hole CH. This pixelelectrode PE is formed of a transparent, electrically conductivematerial such as ITO or IZO. The pixel electrode PE is covered with thefirst vertical alignment film AL1.

On the other hand, the counter-substrate CT is formed by using a secondinsulative substrate 30 with light transmissivity, such as a glasssubstrate or a resin substrate. The counter-substrate CT includes, onthat side of the second insulative substrate 30, which is opposed to thearray substrate AR, a light-shield layer 31, color filters 32, anovercoat layer 33, a second common electrode CE2, and a second verticalalignment film AL2.

The light-shield layer 31 partitions each pixel PX in the active areaACT, and forms an aperture portion AP. The light-shield layer 31 isprovided at boundaries between color pixels, or at positions opposed tothe source lines provided on the array substrate AR. The light-shieldlayer 31 is formed of a light-shielding metallic material or a blackresin material.

The color filter 32 is formed in the aperture portion AP, and a partthereof overlaps the light-shield layer 31. The color filters 32 includea red color filter formed of a resin material which is colored in red, agreen color filter formed of a resin material which is colored in green,and a blue color filter formed of a resin material which is colored inblue. The red color filter is disposed in a red color pixel whichdisplays red, the green color filter is disposed in a green color pixelwhich displays green, and the blue color filter is disposed in a bluecolor pixel which displays blue. In addition, a white (or transparent)color filter is disposed in a white color pixel which displays white.Incidentally, no color filter may be disposed in the white color pixel.Besides, the white color filter may not strictly be an achromatic colorfilter, and may be a color filter which is lightly colored (e.g. coloredin light yellow). Boundaries between the color filters 32 of differentcolors are located at positions overlapping the light-shield layer 31above the source lines S.

The overcoat layer 33 covers the color filters 32. The overcoat layer 33planarizes asperities of the light-shield layer 31 and color filters 32.The overcoat layer 33 is formed of, for example, a transparent resinmaterial. This overcoat layer 33 serves as an underlayer of the secondcommon electrode CE2.

The second common electrode CE2 is formed on that side of the overcoatlayer 33, which is opposed to the array substrate AR. As illustrated inthe Figure, the second common electrode CE2 extends above the sourceline S1 and source line S2, and extends toward the neighboring pixels.The second common electrode CE2 is formed of, for example, atransparent, electrically conductive material such as ITO or IZO. Thesecond common electrode CE2 is covered with the second verticalalignment film AL2.

The first vertical alignment film AL1 and second vertical alignment filmAL2 are formed of a material which exhibits vertical alignmentproperties, and have an alignment restriction force which aligns liquidcrystal molecules in a normal direction of the substrate, withoutrequiring alignment treatment such as rubbing.

The above-described array substrate AR and counter-substrate CT aredisposed such that their first vertical alignment film AL1 and secondvertical alignment film AL2 are opposed to each other. In this case, apredetermined cell gap is created between the array substrate AR and thecounter-substrate CT by columnar spacers which are formed on one of thearray substrate AR and counter-substrate CT. The array substrate AR andcounter-substrate CT are attached by a sealant to maintain the cell gaptherebetween. The liquid crystal layer LQ is sealed in the cell gapbetween the first vertical alignment film AL1 and second verticalalignment film AL2. This liquid crystal layer LQ is composed of a liquidcrystal composition with a negative dielectric constant anisotropy(negative-type).

A backlight unit BL is disposed on the back side of the liquid crystaldisplay panel LPN having the above-described structure. Various modesare applicable to the backlight unit BL, but detailed descriptions ofthe backlight unit BL are omitted.

A first optical element OD1 including a first polarizer PL1 is disposedon an outer surface 10B of the first insulative substrate 10. A secondoptical element OD2 including a second polarizer PL2 is disposed on anouter surface 30B of the second insulative substrate 30. The firstpolarizer PL1 and second polarizer PL2 are disposed, for example, in apositional relationship of crossed Nicols in which their polarizationaxes are perpendicular to each other.

FIG. 5 is a plan view which schematically illustrates an example of alayout of pixels and color filters in the embodiment. In this example,the first direction X and second direction Y are perpendicular to eachother.

A unit pixel for realizing color display is composed of a plurality ofdifferent color pixels. The unit pixel is a minimum unit whichconstitutes a color image that is displayed on the active area. In theexample illustrated, the unit pixel UP is composed of six color pixels.Specifically, the unit pixel UP1 is composed of a color pixel (firstcolor pixel) PX11, a color pixel (second color pixel) PX12, a colorpixel (third color pixel) PX13, a color pixel (fourth color pixel) PX14,a color pixel (fifth color pixel) PX15 and a color pixel (sixth colorpixel) PX16. In the Figure, each color pixel has a rectangular shapewith a pair of short sides in the first direction X, and a pair of longsides in the second direction Y, and each color pixel is indicated by aone-dot-and-dash line. The color pixel PX11 is a red color pixel. Thecolor pixel PX12 is a green color pixel neighboring the color pixel PX11in the first direction X. The color pixel PX13 is a blue color pixelneighboring the color pixel PX12 in the first direction X. The colorpixel PX14 is a red color pixel neighboring the color pixel PX11 in thesecond direction Y. The color pixel PX15 is a green color pixelneighboring the color pixel PX12 in the second direction Y. The colorpixel PX16 is a white color pixel neighboring the color pixel PX13 inthe second direction Y.

Each of the color pixel PX11, color pixel PX12, color pixel PX14 andcolor pixel PX15 has a long-side length L1 in the second direction Y.The color pixel PX13 has a long-side length L2 in the second directionY, which is greater than the long-side length L1. The color pixel PX16has a long-side length L3 in the second direction Y, which is less thanthe long-side length L1. Each of the color pixel PX11, color pixel PX12,color pixel PX14 and color pixel PX15 has a short-side length S1 in thefirst direction X. Each of the color pixel PX13 and color pixel PX16 hasa second short-side length S2 in the first direction X, which is greaterthan the short-side length S1.

In this structure, the color pixel PX11, color pixel PX12, color pixelPX14 and color pixel PX15 are substantially equal in area. The area ofthe color pixel PX13 is greater than the area of the color pixel PX11,etc., and is largest in the unit pixel UP1. The area of the color pixelPX16 is less than the area of the color pixel PX11, etc., and issmallest in the unit pixel UP1.

Light-shield layers 31 are disposed at boundaries of the respectivecolor pixels. Each light-shield layer 31 extends linearly in the seconddirection Y. Incidentally, no light-shield layer 31 is disposed at aboundary between color pixels of the same color. Specifically, nolight-shield layer 31 is disposed at a boundary between the color pixelPX11 and color pixel PX14, or between the color pixel PX12 and colorpixel PX15. The light-shield layer 31 is disposed at a boundary betweencolor pixels of different colors. Specifically, the light-shield layer31 extending linearly in the first direction X is disposed at a boundarybetween the color pixel PX13 and color pixel PX16. Thus, each of thecolor pixel PX13 and color pixel PX16 is surrounded by the light-shieldlayers 31.

A color filter (first color filter) 32R is formed in a strip shapeextending in the second direction Y, and is disposed to correspond tothe color pixel PX11 and the color pixel PX14. A color filter (secondcolor filter) 32G neighbors the color filter 32R in the first directionX, is formed in a strip shape extending in the second direction Y, andis disposed to correspond to the color pixel PX12 and the color pixelPX15. A color filter (third color filter) 32B neighbors the color filter32G in the first direction X, is formed in an island shape, and isdisposed to correspond to the color pixel PX13. A color filter (fourthcolor filter) 32W neighbors the color filter 32B in the second directionY, neighbors the color filter 32G in the first direction X, is formed inan island shape, and is disposed to correspond to the color pixel PX16.The color filter 32B and color filter 32W are alternately disposed inthe second direction Y.

The color filter 32R and color filter 32G have an equal width in thefirst direction X. The color filter 32B and color filter 32W have anequal width in the first direction X, and this width is greater than thewidth of the color filter 32R, etc.

The color filter 32R is a red (R) color filter. The color filter 32G isa green (G) color filter. The color filter 32B is a blue (B) colorfilter. The color filter 32W is a white (W) color filter. The first tofourth color filters have mutually neighboring end portions overlappingthe light-shield layers 31.

In this manner, the active area includes the color pixels of the fourcolors (red color pixels, green color pixels, blue color pixels, andwhite color pixels), and the number of color pixels of two colors (inthe illustrated example, blue color pixels and white color pixels) ofthe four colors is half the number of color pixels of the other twocolors (in the illustrated example, red color pixels and green colorpixels). In addition, the long-side length of the color pixels, thenumber of which is smaller, is different from the long-side length ofthe color pixels, the number of which is larger. Furthermore, theshort-side length of the color pixels, the number of which is smaller,is different from the short-side length of the color pixels, the numberof which is larger.

For example, the sum of the areas of the color pixel PX11 and colorpixel PX14, which are red color pixels, is equal to the sum of the areasof the color pixel PX12 and color pixel PX15, which are green colorpixels, and is equal to the area of the color pixel PX13 which is bluecolor pixel. However, the area of each color pixel may be varied byaltering the long-side length and short-side length of the color pixelin accordance with the transmittance of each of the color filter 32Rwhich is applied to the red color pixel, the color filter 32G which isapplied to green color pixel, and the color filter 32B which is appliedto blue color pixel. In the case where the transmittance of the colorfilter 32B is higher than the transmittance of the color filter 32R andcolor filter 32G, the area of the color pixel PX13 may be made smallerthan the sum of the areas of the color pixel PX11 and color pixel PX14which are red color pixels.

FIG. 6 is a plan view which schematically illustrates a structureexample of an array substrate AR to which the color filters shown inFIG. 5 are applied. In this example, only the structure of the arraysubstrate AR, which is necessary for the description, is illustrated,and depiction of the first common electrode, etc. is omitted.

A gate line G1 extends in the first direction X and crosses centralportions of the color pixel PX11, color pixel PX12, and color pixelPX13. A gate line G2 extends in the first direction X and crosses thecentral portions of the color pixel PX14, color pixel PX15, and colorpixel PX16.

A pixel electrode (first pixel electrode) PE11 is disposed to correspondto the color pixel PX11, and is connected to a source line S1 via aswitching element which is connected to the gate line G1. A pixelelectrode (second pixel electrode) PE12 is disposed to correspond to thecolor pixel PX12 and neighbors the pixel electrode PE11 in the firstdirection X. The pixel electrode PE12 is connected to a source line S2via a switching element which is connected to the gate line G1. A pixelelectrode (third pixel electrode) PE13 is disposed to correspond to thecolor pixel PX13 and neighbors the pixel electrode PE12 in the firstdirection X. The pixel electrode PE13 is connected to a source line S3via a switching element which is connected to the gate line G1. A pixelelectrode (fourth pixel electrode) PE14 is disposed to correspond to thecolor pixel PX14 and neighbors the pixel electrode PE11 in the seconddirection Y. The pixel electrode PE14 is connected to the source line S1via a switching element which is connected to a gate line G2. A pixelelectrode (fifth pixel electrode) PE15 is disposed to correspond to thecolor pixel PX15 and neighbors the pixel electrode PE12 in the seconddirection Y. The pixel electrode PE15 is connected to the source line S2via a switching element which is connected to the gate line G2. A pixelelectrode (sixth pixel electrode) PE16 is disposed to correspond to thecolor pixel PX16 and neighbors the pixel electrode PE13 in the seconddirection Y. The pixel electrode PE16 is connected to the source line S3via a switching element which is connected to the gate line G2.

Each of the pixel electrode PE11, pixel electrode PE12, pixel electrodePE14 and pixel electrode PE15 has a long-side length L11 in the seconddirection Y. The pixel electrode PE13 has a long-side length L12 in thesecond direction Y, which is greater than the long-side length L11. Thepixel electrode PE16 has a long-side length L13 in the second directionY, which is less than the long-side length L11. Each of the pixelelectrode PE11, pixel electrode PE12, pixel electrode PE14 and pixelelectrode PE15 has a short-side length S11 in the first direction X.Each of the pixel electrode PE13 and pixel electrode PE16 has ashort-side length S12 in the first direction X, which is greater thanthe short-side length S11.

The pixel electrode PE11 and pixel electrode PE14 arranged in the seconddirection Y are opposed to the color filter 32R shown in FIG. 5. Thepixel electrode PE12 and pixel electrode PE15 arranged in the seconddirection Y are opposed to the color filter 32G shown in FIG. 5. Thepixel electrode PE13 is opposed to the color filter 32B shown in FIG. 5.The pixel electrode PE16 is opposed to the color filter 32W shown inFIG. 5.

FIG. 7 is a plan view which schematically illustrates a structureexample of the second common electrode CE2 which is disposed to beopposed to the array substrate AR shown in FIG. 6.

The second common electrode CE2 is opposed to the pixel electrodes PE11to PE16. Slits SL are formed in the second common electrode CE2 atpositions opposed to the pixel electrodes PE11 to PE16, respectively.The slits SL have substantially the same shape. In the exampleillustrated, each slit SL has a vertically elongated shape extending inthe second direction Y.

Next, the operation of the display device in the embodiment isdescribed.

In an OFF state in which no potential difference is produced between thepixel electrode PE and the first common electrode CE1 and second commonelectrode CE2 (i.e. a state in which no voltage is applied to the liquidcrystal layer LQ), no electric field is produced between the pixelelectrode PE and second common electrode CE2. Thus, as illustrated inFIG. 4, liquid crystal molecules LM included in the liquid crystal layerLQ are initially aligned substantially perpendicular to the substratemajor surface (X-Y plane) between the first vertical alignment film AL1and second vertical alignment film AL2. In this case, part of linearlypolarized light from the backlight unit BL passes through the firstpolarizer PL1 and enters the liquid crystal display panel LPN. Thepolarization state of the linearly polarized light, which enters theliquid crystal display panel LPN, hardly varies when the light passesthrough the liquid crystal layer LQ. Thus, the linearly polarized lightemerging from the liquid crystal display panel LPN is absorbed by thesecond polarizer PL2 that is in the positional relationship of crossedNicols in relation to the first polarizer PL1 (black display).

In an ON state in which a potential difference is produced between thepixel electrode PE and the first common electrode CE1 and second commonelectrode CE2 (i.e. a state in which a voltage is applied to the liquidcrystal layer LQ), a vertical electric field or an inclined electricfield avoiding the slits SL is produced between the pixel electrode PEand second common electrode CE2. Thus, the liquid crystal molecules LMare aligned in a direction which is different from the initial alignmentdirection, by the effect of the vertical electric field or inclinedelectric field. Specifically, since negative-type liquid crystalmolecules LM are aligned such that their major axes cross the electricfield, the liquid crystal molecules LM are aligned in the ON state in anoblique direction or in a horizontal direction, relative to thesubstrate major surface.

In this ON state, the polarization state of the linearly polarizedlight, which enters the liquid crystal display panel LPN, variesdepending on the alignment state of the liquid crystal molecules LM (orthe retardation of the liquid crystal layer) when the light passesthrough the liquid crystal layer LQ. Thus, in the ON state, at leastpart of the light emerging from the liquid crystal layer LQ passesthrough the second polarizer PL2 (white display).

In addition, in the ON state, a storage capacitance CS is formed by thepixel electrode PE and the first common electrode CE1 that are opposedto each other via the fourth insulating film 14, and retains a necessarycapacitance for displaying an image. Specifically, a pixel potential,which has been written to each pixel via the switching element SW, isretained in the storage capacitance CS for a predetermined period.

Here, in the VA mode, the hue of the liquid crystal layer LQ changesdepending on the alignment of liquid crystal molecules LM affected byoptical rotatory dispersion (or wavelength dispersion) in the liquidcrystal layer LQ. That is, although the liquid crystal layer LQ itselfis originally transparent, the alignment of liquid crystal molecules LMmay change the color of the liquid crystal layer LQ bluish. Thus, inorder to maintain a white balance, a voltage value is adjusted tocorrespond to the gradation values in the pixels of each of the primarycolors of red, green and blue. On the other hand, the bluish color ofthe liquid crystal layer LQ itself appears conspicuously in the whitecolor pixels and it is not sufficiently suppressed by adjusting thechromaticity of the other color pixels.

FIG. 8 is a view which conceptually illustrates a shift in chromaticityrelative to applied voltages in white color pixels.

The horizontal axis of the graph indicates voltage applied to the liquidcrystal layer LQ, and the vertical axis of the graph indicates shift Δxin coordinate x and shift Δy in coordinate y in the chromaticitydiagram. Note that shift Δx and shift Δy do not always agree but vary ina similar manner.

In the VA mode, if the voltage value applied to the white color pixelsis set to correspond to each gradation value within the same voltagerange as that of red and green color pixels and is changed from topvoltage Vt1 corresponding to the maximum gradation value 255 (white) tobottom voltage Vb corresponding to minimum gradation value 0 (black),both shifts Δx and Δy significantly decline. That is, if the voltagevalue applied to the liquid crystal layer LQ is changed from top voltageVt1 to bottom voltage Vb, the chromaticity of the white color pixelsshifts greatly from white to blue in the chromaticity diagram. Thisphenomenon is referred to as the blue shift.

For example, a comparative example was prepared to have a voltage rangeof 4.6 V in which bottom voltage Vb is 0 and top voltage Vt1 is 4.6 Vwas set in all of red, green, blue and white color pixels, and thevoltage value was changed therein from top voltage Vt1 to bottom voltageVb. Consequently, it showed shift n1 in the chromaticity in the whitecolor pixels.

Note that the Figure shows a shift in the chromaticity relative to theapplied voltage to white color pixels in the IPS mode for referencepurpose only. In the IPS mode, if the voltage value is changed from topvoltage Vt1 to bottom voltage Vb with the same voltage setting as in theVA mode, the shift in the chromaticity in the white color pixels is lessthan that of the VA mode. From this point, it is acknowledged that theVA mode has the property of showing the blue shift more conspicuouslythan the IPS mode.

Therefore, in the embodiment, the top voltage applied to the white colorpixels corresponding to the maximum gradation value is set less than thetop voltage applied to each of red and green color pixels correspondingto the maximum gradation value. For example, as illustrated in theFigure, the top voltage of each of red and green color pixels is set tovoltage value Vt1 while the top voltage of the white color pixels is setto voltage value Vt2. The bottom voltage is set to Vb in the Figure inevery pixel. That is, the voltage range allocated to the gradationvalues from the minimum to the maximum in the red and green color pixelsis a range of bottom voltage Vb to top voltage Vt1 while the voltagerange allocated to gradation values from the minimum to the maximum inthe white color pixels is a range of bottom voltage Vb to top voltageVt2, which is less than that of each of red and green color pixels.

In this voltage setting, if the voltage value is changed from topvoltage Vt2 to bottom voltage Vb in the white color pixels, the shift inthe chromaticity therein is maintained as Δ2 which is less than Δ1. Inother words, by setting the top voltage and the voltage range of thewhite color pixels to be less than those of the red and green colorpixels, the blue shift in the white color pixels can be suppressed.

For example, example 1 was prepared to have a voltage range of 4.6 V inwhich bottom voltage Vb is 0 and top voltage Vt1 is 4.6 V was set in thered, green, and blue color pixels and a voltage range of 3.5 V in whichbottom voltage Vb is 0 and top voltage Vt2 is 3.5 V in the white colorpixels. The voltage value was changed while a white image was beingdisplayed on the active area and the changes in the chromaticity weremeasured by a chromaticity meter. Consequently, example 1 showed achromaticity change which is less than that in the comparative example,and was proved to be able to suppress the blue shift.

Note that, if the top voltage is set to Vt2 which is less than Vt1 inthe white color pixels, the chromaticity shifts to blue by a differencetherebetween (Δ1−Δ2). Such a difference in the chromaticity can becompensated by, for example, adjusting a cell gap pixel by pixel, or canbe compensated by a hue of a color filter applied to the white colorpixels (for example, yellow which is a complementary color of blue).

The above-mentioned blue shift is a phenomenon in which the liquidcrystal layer LQ itself is colored bluish and it is observed not only inthe white color pixels but also in the red, green and blue color pixels.Thus, the same method used for the white color pixels can be applied tothe blue color pixels.

Specifically, not only as to the white color pixels, the top voltageapplied to the blue color pixels corresponding to the maximum gradationvalue may also be set less than the top voltage applied to each of redand green color pixels corresponding to the maximum gradation value. Forexample, as illustrated in the Figure, the top voltage of each of redand green color pixels is set to voltage value Vt1 while the top voltageof each of white and blue color pixels is set to voltage value Vt2. Thebottom voltage is set to Vb in the Figure in every pixel. That is, thevoltage range allocated to gradation values from the minimum to themaximum in the white and blue color pixels is a range of bottom voltageVb to top voltage Vt2, which is less than that of each of red and greencolor pixels.

In this voltage setting, if the voltage value is changed from topvoltage Vt2 to bottom voltage Vb in the white and blue color pixels, theblue shift in the white and blue color pixels can be suppressed. Forexample, example 2 was prepared to have a voltage range of 4.6 V inwhich bottom voltage Vb is 0 and top voltage Vt1 is 4.6 V was set in thered and green color pixels and a voltage range of 3.5 V in which bottomvoltage Vb is 0 and top voltage Vt2 is 3.5 V in the white and blue colorpixels. The voltage value was changed while a white image was beingdisplayed on the active area and the changes in the chromaticity weremeasured by a chromaticity meter. Consequently, Example 2 showed achromaticity change which is less than that of example 1, and was provedto be able to further suppress the blue shift.

As can be understood from the above, in the embodiment, a shift in thechromaticity caused by a voltage applied to a liquid crystal layer canbe suppressed. Furthermore, since a unit pixel is composed of four colorpixels of red, green, blue and white, the display luminance per unitpixel can be improved as compared to a case where a unit pixel iscomposed of three color pixels of red, green, and blue. In addition, bysubstituting the display luminance of the white color pixels for thetotal display luminance produced by the red, green and blue colorpixels, the display luminance of the unit pixels increases. Thus, theluminance of the backlight unit can be reduced by that degree, and thepower consumption can be reduced. Furthermore, by virtue of the highluminance of the unit pixels, the visibility of a display image can beenhanced even in ambient light. In addition, since the pixel size of thewhite color pixel does not excessively increase, the white color pixelsthemselves are less easily discernible even when an image with a highdisplay luminance is displayed by the white color pixels. Therefore, thedisplay quality can be improved.

According to the embodiment, the capacitance, which is necessary fordisplaying an image in each pixel, can be formed by the pixel electrodePE and first common electrode CE1 which are opposed via the fourthinsulating film 14. Thus, when the capacitance is formed, a wiring lineor electrode, which crosses the pixel and is formed of a light-shieldingwiring material, is unnecessary. In addition, the fourth insulating film14 is formed to have a smaller film thickness than the third insulatingfilm that is formed of a resin material or the like. Therefore, arelatively large capacitance can easily be formed by the pixel electrodePE and first common electrode CE1 which are disposed via the fourthinsulating film 14.

Moreover, since each of the pixel electrode PE and first commonelectrode CE1 is formed of a transparent, electrically conductivematerial, an area overlapping the pixel electrode PE and first commonelectrode CE1 contributes to display. Thus, compared to a comparativeexample in which a storage capacitance line crossing the pixel isdisposed, the aperture ratio, transmittance or luminance per pixel,which contributes to display, can be improved. Therefore, while thecapacitance necessary for display is secured, the display quality can beimproved.

In addition, the first common electrode CE1 extends above the sourceline S1 and source line S2. Thus, in the ON state, an undesired leakelectric field from the source line toward the liquid crystal layer LQcan be shielded by the first common electrode CE1. Specifically, it ispossible to suppress formation of an undesired electric field or anundesired capacitance between the source line and the pixel electrode PEor second common electrode CE2, and to suppress disturbance in alignmentof liquid crystal molecules LM in an area overlapping the source line.

Furthermore, the liquid crystal molecules LM in the area overlapping thesource line maintains the initial alignment state even in the ON state,since the first common electrode CE1 and second common electrode CE2 arekept at the same potential. Therefore, pixel electrodes PE neighboringin the first direction X can be located closer to each other up to aprocessing limit, and the area which contributes to display per pixelcan be further increased.

In addition, even when one of the pixels neighboring with the sourceline interposed is in the ON state and the other is in the OFF state, nopotential difference occurs by means of the first common electrode CE1and second common electrode CE2, in the liquid crystal layer on thesource line between the ON-state pixel and OFF-state pixel. Thus, theliquid crystal molecules LM in the area overlapping the source line arekept in the initial alignment state. Therefore, even when the liquidcrystal display panel LPN is viewed in an oblique direction, degradationin display quality due to color mixing can be suppressed. In addition,since there is no need to increase the width of the light-shield layer31 in order to prevent color mixing, the area contributing to displayper pixel can be further increased.

Next, modifications will be described.

FIG. 9 is a plan view which schematically shows another structureexample of a layout of pixels and color filters in the embodiment.

The structure example shown in FIG. 9 differs from the structure exampleshown in FIG. 5 in respect of the unit pixel UP composed of four colorpixels. That is, the unit pixel UP is composed of a color pixel (firstcolor pixel) PX11, a color pixel (second color pixel) PX12, a colorpixel (third color pixel) PX13, and a color pixel (fourth color pixel)PX14. The color pixel PX11 is a red color pixel. The color pixel PX12 isa green color pixel neighboring the color pixel 11 in the firstdirection X. The color pixel PX13 is a blue color pixel neighboring thecolor pixel PX12 in the first direction X. The color pixel PX14 is awhite color pixel neighboring the color pixel PX13 in the firstdirection X.

Each of the color pixel PX11, color pixel PX12, color pixel PX13, andcolor pixel PX14 has a long-side length L1 in the second direction Y anda short-side length S1 in the first direction X. Light-shield layers 31are disposed at boundaries of the respective color pixels. Eachlight-shield layer 31 extends linearly in the second direction Y.

A color filter (first color filter) 32R is a red (R) color filterdisposed to correspond to the color pixel PX11. A color filter (secondcolor filter) 32G is a green (G) color filter disposed to correspond tothe color pixel PX12. A color filter (third color filter) 32B is a blue(B) color filter disposed to correspond to the color pixel PX13. A colorfilter (fourth color filter) 32W is a white (W) color filter disposed tocorrespond to the color pixel PX14.

In such a layout, too, by using the same voltage setting as in theabove-described example, the same advantageous effects therein can beobtained.

FIG. 10 is a plan view which schematically shows another structureexample of a layout of pixels and color filters in the embodiment.

The structure example shown in FIG. 10 differs from the structureexample shown in FIG. 5 in respect of the unit pixel UP composed ofeight color pixels. That is, the unit pixel UP is composed of a colorpixel (first color pixel) PX11, a color pixel (second color pixel) PX12,a color pixel (third color pixel) PX13, a color pixel (fourth colorpixel) PX14, a color pixel (fifth color pixel) PX15, a color pixel(sixth color pixel) PX16, a color pixel (seventh color pixel) PX17, anda color pixel (eighth color pixel) PX18. The color pixel (first colorpixel) PX11, color pixel (second color pixel) PX12, color pixel (thirdcolor pixel) PX13, and color pixel (fourth color pixel) PX14 are alignedin this order in the first direction X. The color pixel (fifth colorpixel) PX15, color pixel (sixth color pixel) PX16, color pixel (seventhcolor pixel) PX17, and color pixel (eighth color pixel) PX18 are alignedin this order in the first direction X. The color pixels PX11 and PX17are red color pixels. The color pixels PX12 and PX18 are green colorpixels. The color pixels PX13 and PX15 are blue color pixels. The colorpixels PX14 and PX16 are white color pixels. Light-shield layers 31 aredisposed at boundaries of the respective color pixels.

A color filter (first color filter) 32R is a red (R) color filterdisposed to correspond to the color pixel PX11. A color filter (secondcolor filter) 32G is a green (G) color filter disposed to correspond tothe color pixel PX12. A color filter (third color filter) 32B is a blue(B) color filter disposed to correspond to the color pixel PX13. A colorfilter (fourth color filter) 32W is a white (W) color filter disposed tocorrespond to the color pixel PX14. A color filter (fifth color filter)32B is a blue (B) color filter disposed to correspond to the color pixelPX15. A color filter (sixth color filter) 32W is a white (W) colorfilter disposed to correspond to the color pixel PX16. A color filter(seventh color filter) 32R is a red (R) color filter disposed tocorrespond to the color pixel PX17. A color filter (eighth color filter)32G is a green (G) color filter disposed to correspond to the colorpixel PX18.

In such a layout, too, by using the same voltage setting as in theabove-described example, the same advantageous effects therein can beobtained.

As has been described above, according to the present embodiment, adisplay device, which can improve display quality, can be provided.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A display device comprising: a first substrateincluding a first pixel electrode disposed on a first color pixel ofred, a second pixel electrode disposed on a second color pixel of green,a third pixel electrode disposed on a third color pixel of blue, and afourth pixel electrode disposed on a fourth color pixel of white; asecond substrate including a common electrode which is opposed to thefirst, second, third, and fourth pixel electrodes; and a liquid crystallayer held between the first substrate and the second substrate, whereina top voltage applied to the fourth color pixel to correspond to amaximum gradation value is set to be less than a top voltage applied toeach of the first color pixel and the second color pixel to correspondto respective maximum gradation values.
 2. The display device of claim1, wherein a voltage range of a minimum gradation value to a maximumgradation value of the fourth color pixel is set to be less than avoltage range of a minimum gradation value to a maximum gradation valueof each of the first color pixel and the second color pixel.
 3. Thedisplay device of claim 1, wherein a top voltage applied to the thirdcolor pixel to correspond to a maximum gradation value is set to be lessthan the top voltage applied to each of the first color pixel and thesecond color pixel to correspond to the respective maximum gradationvalues.
 4. The display device of claim 3, wherein a voltage range of aminimum gradation value to a maximum gradation value of the third colorpixel is set to be less than the voltage range of the minimum gradationvalue to the maximum gradation value of each of the first color pixeland the second color pixel.
 5. The display device of claim 1, whereinthe first color pixel, the second color pixel, and the third color pixelare aligned in the order stated in a first direction, and the thirdcolor pixel and the fourth color pixel are aligned in a second directionwhich is perpendicular to the first direction.
 6. The display device ofclaim 5, wherein the first substrate further comprises a fifth pixelelectrode disposed on a fifth color pixel of red which is adjacent tothe first color pixel in the second direction, and a sixth pixelelectrode disposed on a sixth color pixel of green which is adjacent tothe second color pixel in the second direction.
 7. The display device ofclaim 1, wherein the first color pixel, the second color pixel, thethird color pixel, and the fourth color pixel are aligned in the orderstated in the first direction.
 8. The display device of claim 7, whereinthe first substrate further includes a fifth pixel electrode disposed ona fifth color pixel of blue which is adjacent to the first color pixelin the second direction, a sixth pixel electrode disposed on a sixthcolor pixel of white which is adjacent to the second color pixel in thesecond direction, a seventh pixel electrode disposed on a seventh colorpixel of red which is adjacent to the third color pixel in the seconddirection, and eighth pixel electrode disposed on a eighth color pixelof green which is adjacent to the fourth color pixel in the seconddirection.
 9. A display device comprising: a first substrate including afirst common electrode, an interlayer insulating film covering the firstcommon electrode, a first pixel electrode disposed on a first colorpixel of red on the interlayer insulating film, a second pixel electrodedisposed on a second color pixel of green on the interlayer insulatingfilm, a third pixel electrode disposed on a third color pixel of blue onthe interlayer insulating film, and a fourth pixel electrode disposed ona fourth color pixel of white on the interlayer insulating film; asecond substrate including a second common electrode which is opposed tothe first pixel electrode, the second pixel electrode, the third pixelelectrode, and the fourth pixel electrode; and a liquid crystal layerheld between the first substrate and the second substrate, wherein a topvoltage applied to the fourth color pixel to correspond to a maximumgradation value is set to be less than a top voltage applied to each ofthe first color pixel and the second color pixel to correspond torespective maximum gradation values.
 10. The display device of claim 9,wherein a voltage range of a minimum gradation value to a maximumgradation value of the fourth color pixel is set to be less than avoltage range of a minimum gradation value to a maximum gradation valueof each of the first color pixel and the second color pixel.
 11. Thedisplay device of claim 9, wherein a top voltage applied to the thirdcolor pixel to correspond to a maximum gradation value is set to be lessthan the top voltage applied to each of the first color pixel and thesecond color pixel to correspond to the respective maximum gradationvalues.
 12. The display device of claim 11, wherein a voltage range of aminimum gradation value to a maximum gradation value of the third colorpixel is set to be less than the voltage range of the minimum gradationvalue to the maximum gradation value of each of the first color pixeland the second color pixel.
 13. The display device of claim 9, whereinthe first color pixel, the second color pixel, and the third color pixelare aligned in the order stated in a first direction, and the thirdcolor pixel and the fourth color pixel are aligned in a second directionwhich is orthogonal to the first direction.
 14. The display device ofclaim 13, wherein the first substrate further comprises a fifth pixelelectrode disposed on a fifth color pixel of red which is adjacent tothe first color pixel in the second direction, and a sixth pixelelectrode disposed on a sixth color pixel of green which is adjacent tothe second color pixel in the second direction.
 15. The display deviceof claim 9, wherein the first color pixel, the second color pixel, thethird color pixel, and the fourth color pixel are aligned in the orderstated in the first direction.
 16. The display device of claim 15,wherein the first substrate further includes a fifth pixel electrodedisposed on a fifth color pixel of blue which is adjacent to the firstcolor pixel in the second direction, a sixth pixel electrode disposed ona sixth color pixel of white which is adjacent to the second color pixelin the second direction, a seventh pixel electrode disposed on a seventhcolor pixel of red which is adjacent to the third color pixel in thesecond direction, and eighth pixel electrode disposed on a eighth colorpixel of green which is adjacent to the fourth color pixel in the seconddirection.
 17. The display device of claim 9, wherein the firstsubstrate further comprises a first vertical alignment film covering thefirst to fourth pixel electrodes, the second substrate further includesa second vertical alignment film covering the common electrode, and theliquid crystal layer is held between the first vertical alignment filmand the second vertical alignment film.
 18. The display device of claim9, wherein the interlayer insulating film is formed of an inorganicmaterial.